A motion transmission system in a bicycle comprises a chain extending between toothed wheels associated with the axle of the pedal cranks and with the hub of the rear wheel. When there is more than one toothed wheel at at least one of the axle of the pedal cranks and the hub of the rear wheel, and the motion transmission system is therefore provided with a gearshift, a front derailleur and/or a rear derailleur are provided for. In the case of an electronically servo-assisted gearshift, each derailleur comprises a chain guide element, also known as cage, movable to move the chain among the toothed wheels in order to change the gear ratio, and an electromechanical actuator to move the chain guide element. The actuator in turn typically comprises a motor, typically an electric motor, coupled with the chain guide element through a linkage such as an articulated parallelogram, a rack system or a worm screw system, as well as a sensor of the position, speed and/or acceleration of the rotor or of any moving part downstream of the rotor, down to the chain guide element itself. It is worthwhile noting that slightly different terminology from that used in this context is also in use.
Control electronics changes the gear ratio automatically, for example based on one or more detected variables, such as the travel speed, the cadence of rotation of the pedal cranks, the torque applied to the pedal cranks, the slope of the travel terrain, the heart rate of the cyclist and similar, and/or, of particular interest for the present invention, based on commands manually input by the cyclist through suitable control members, for example levers and/or buttons.
By convention, downward gearshifting is said when the chain passes from a toothed wheel of greater diameter to a toothed wheel of smaller diameter, and upward gearshifting when the chain moves from a toothed wheel of smaller diameter to a toothed wheel of greater diameter. Concerning this, it should be noted that in a front gearshift group, downward gearshifting corresponds to passing to a lower gear ratio and upward gearshifting corresponds to the passage to a higher gear ratio; vice-versa in a rear gearshift group, downward gearshifting corresponds to the passage to a higher gear ratio and upward gearshifting corresponds to the passage to a lower gear ratio.
A device for controlling the front derailleur and a device for controlling the rear derailleur—or only one of the two in the case of simpler gearshifts—are mounted so as to be easily maneuvered by the cyclist, normally on the handlebars, close to the handgrips thereof where the brake lever is also located for controlling the brake of the front and rear wheel, respectively. Control devices that allow to drive both a derailleur in the two directions and a brake are commonly called integrated controls.
By convention, the control device of the front derailleur and the brake lever of the front wheel are located close to the left handgrip, and vice-versa the control device of the rear derailleur and the brake lever of the rear wheel are located close to the right handgrip.
During travel, there is sometimes a need (detected by electronics or by the cyclist) or a wish of the cyclist to carry out multiple gearshifting, in other words to move the chain from the toothed wheel (of the rear or front gearshift group) with which it is engaged—or starting gear wheel—to a toothed wheel not immediately adjacent thereto, having a greater diameter (multiple upward gearshifting) or having a smaller diameter (multiple downward gearshifting).
WO 2007/083331 A1 discloses a mechanical bicycle gearshift that allows manual input of upward and downward gearshifting commands through the manual actuation of a single lever in a same direction, by two different angles of rotation.
The technical problem at the basis of the invention is to provide a method for electronically controlling a bicycle gearshift, and an electronically servo-assisted bicycle gearshift that allow manual input of upward and downward gearshifting commands through the manual actuation of a single lever in a same direction, by two different strokes (different angles of rotation).